California’s Strict New Booster Seat Law Offers Scant Evidence It Improves Child Rider Safety

When Assemblywoman Lori Wilson first proposed updating California’s booster seat law, she imagined a modest, commonsense safety measure supported by crash data and automotive experts. Instead, the bill quickly veered into what critics called legislative overreach, with early drafts suggesting that eighth graders could be forced into booster seats and that high school sophomores — those old enough to obtain a learner’s permit or driver’s license — could be banned from sitting in the front seat. Lawmakers and the public balked at the idea. What began as a safety tweak turned into a headline-grabbing controversy over how far California should go to regulate kids in cars.Ms. Wilson, a Democrat, said part of the initial resistance to her booster seat bill stemmed from an unrelated debate over limiting penalties for sex solicitation with 16 and 17 year olds. Republicans blasted Democrats over political inconsistency between the two bills. Parents also pushed back against proposals that could have forced older children into booster seats. Several Democrats with children chose not to vote rather than publicly oppose the bill.Lawmakers raised other concerns during the monthslong debate: Stockton Assemblywoman Rhodesia Ransom warned the proposed standards could give police pretexts to pull over people of color and questioned how subjective assessments on right-sizing teens would work in practice. Rural legislators, including Republican Heather Hadwick, similarly questioned enforcement for families in pickup trucks and other real-world settings.In June, Ms. Wilson brought a revised version back. After removing the most controversial provisions, Assembly Bill 435 passed and was signed into law Governor Gavin Newsom in October 2025. The new law, effective January 1, 2027, keeps existing booster requirements — children must use boosters until age 8 or 4- foot- 9 . It also adds a size-based, five-step fit test for ages eight to 16 to determine whether a seatbelt fits properly. Children and teens up to age 16 must be able to pass the test before graduating from booster seats or to sit in the front seat of a vehicle. The five-step test asks whether a child can sit all the way back on a seat with knees bent at the edge; have the shoulder belt between neck and arm; have the lap belt low against the thigh; and maintain the position comfortably for the whole trip. Drivers unable to affirm all five could face fines up to $490 if they are pulled over.Safety groups, including AAA, the National Highway Transportation Safety Administration, and the California Department of Public Health, supported the measure, citing data that proper restraints reduce child injury risk by more than 80 percent.Yet the scientific foundation for the five-step test itself remains contested. “The reality check behind California’s law is that there is no body of scientific research underpinning the five-step child passenger safety test,” California-based risk analyst Dennis Santiago tells The New York Sun. Mr. Santiago notes that federal research decades ago established a body of crash-injury biomechanics research that was used to develop recommendations on the use of safety restraints for people under 57 inches and 8-12 years old. But that does not address the state’s new fit test.The five-step seatbelt fit test represents “an argument for common sense based on a perception by special interest groups that people do not fit the statistical average criteria of established federal analysis,” Mr. Santiago says. He adds that the science is missing when it comes to crash injury data comparing outcomes for children using standard seatbelts versus booster seats. “I have not found specific crash data test analysis comparing children who are more than one standard deviation off the federal standard under crash conditions comparing seatbelts and booster seats using rigorous testing methods, which are expensive to do,” he tells the Sun.“All I was able to find were assertions by public interest groups that they had concerns. The fact of the matter is that laws based on the five-step seatbelt fit criteria, while well-meaning, are legislating requirements based on anecdotal notions rather than scientific analytics.”Ms. Wilson, however, emphasizes that the five-step test was designed by the federally mandated state Strategic Highway Safety Plan Occupant Protection Committee to account for varying vehicle interior dimensions, including seat depth, headrest positions, and belt placements that simple height requirements cannot address. Following the MoneyMr. Santiago also raises uncomfortable questions about the law’s true motivation. “When I look at this law, I don’t actually see the safety aspect of it as the central element,” he says. “What I do see is a deliberate creation of a pretext to collect revenues from families. California, as a state, is forever trying to find ways to pass new laws to raise revenue through tax increases and fines. Given the soft ground underpinning the scientific basis for the law, one has to ask if revenue is the actual motivation.”He argues the policy impact falls hardest on working families. “From a public policy perspective, criminalizing parental discretion strikes me as a rather cruel form of predatory practice that is most likely to impact poorer people who would not have the money to repeatedly spend money on child safety equipment tailored for a child during a stage in their life where their physical proportions are rapidly changing,” he says. The revenue question also leads to other uncomfortable considerations that the law may prove costlier to the state than planned. According to Mr. Santiago, the law “forces policymakers to ask several inconvenient questions, not the least of which is should the state of California subsidize the cost of these car seats across the full range of body size variability for people with children that are one standard deviation or greater outside federal standards.”California has a history of pioneering vehicle safety requirements, becoming the first state in 1955 to mandate that new cars be equipped with lap belts and the first in 2002 to pass a booster seat law. Yet even in progressive California, lawmakers face limits on how far they can push protective regulations before bumping against common sense and parental autonomy. For many, Assembly Bill 435 represents the latest example of California lawmakers attempting to extend childhood protections into the teenage years only to face resistance when the practical implications become clear. The image of a high school sophomore strapped into a booster seat may prove a bridge too far, even for many committed to following safety science wherever it leads. “It will be interesting to see if this triggers a lawsuit,” Mr. Santiago says. “I suspect it will.”

California’s Strict New Booster Seat Law Offers Scant Evidence It Improves Child Rider Safety

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